Transmitter capable of reducing local oscillation leakage and in-phase/quadrature-phase (i/q) mismatch and adjusting methods thereof

ABSTRACT

An adjusting method for reducing local oscillation leakage or I/Q mismatch in a transmitter includes the steps of: (a) detecting a current extent of local oscillation leakage or I/Q mismatch; (b) determining if an adjusting direction is correct with reference to the current extent of local oscillation leakage or I/Q mismatch thus detected, maintaining the adjusting direction if correct, and reversing the adjusting direction upon determining that the adjusting direction is incorrect; and (c) adjusting a control signal according to the adjusting direction.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority of Taiwanese Application No. 096135951,filed on Sep. 27, 2007.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a transmitter and an adjusting method thereof,more particularly to a transmitter capable of reducing local oscillationleakage and in-phase/quadrature-phase (I/Q) mismatch, and an adjustingmethod thereof.

2. Description of the Related Art

As shown in FIG. 1, a first conventional direct up-conversiontransmitter includes first and second digital-to-analog converters 11,12, first and second low-pass filters 13, 14, first and second mixers15, 16, an adder 17, a power amplifier 18, and an antenna 19. A digitalbase band signal (BBI_(t)) undergoes in sequence digital-to-analogconversion by the first digital-to-analog converter 11, low-passfiltering by the first low-pass filter 13, and mixing with an in-phaselocal oscillator signal (LOI_(t)) by the first mixer 15 so as togenerate an analog in-phase radio frequency signal (RFI_(t)). Anotherdigital base band signal (BBQ_(t)) undergoes in sequencedigital-to-analog conversion by the second digital-to-analog converter12, low-pass filtering by the second low-pass filter 14, and mixing witha quadrature-phase local oscillator signal (LOQ_(t)) by the second mixer16 so as to generate an analog quadrature-phase radio frequency signal(RFQ_(t)). The analog in-phase radio frequency signal (RFI_(t)) and theanalog quadrature-phase radio frequency signal (RFQ_(t)) are combined bythe adder 17, the result of which is amplified by the power amplifier 18for subsequent transmission via the antenna 19.

Although the ideal phase difference between the in-phase localoscillator signal (LOI_(t)) and the quadrature-phase local oscillatorsignal (LOQ_(t)) is 90 degrees, a phase offset (θ_(t)) exists inpractice. In addition, a gain offset (represented by an amplitude offset(α_(t)) in FIG. 1) exists between the in-phase component blocks(including the first digital-to-analog converter 11 and the firstlow-pass filter 13) and the quadrature-phase component blocks (includingthe second digital-to-analog converter 12 and the second low-pass filter14). This phenomenon is referred to as in-phase/quadrature-phase (I/Q)mismatch or in-phase/quadrature-phase (I/Q) imbalance. Moreover, it ispossible for the in-phase local oscillator signal (LOI_(t)) and thequadrature-phase local oscillator signal (LOQ_(t)) to respectively leakinto the analog in-phase radio frequency signal (RFI_(t)) and the analogquadrature-phase radio frequency signal (RFQ_(t)) through the first andsecond mixers 15, 16, respectively. This phenomenon is called localoscillation leakage or local oscillation feedthrough. The abovementionedI/Q mismatch and local oscillation leakage reduce signal-to-noise ratioof signals transmitted by the first conventional direct up-conversiontransmitter, and eventually result in loss of data.

As shown in FIG. 2, U.S. Pat. No. 6,970,689 discloses a secondconventional transmitter capable of reducing local oscillation leakage.The second conventional transmitter includes a mixer 21, a poweramplifier 22, a signal strength measuring circuit 23, and a controlsignal generating circuit 24. The mixer 21 is operable is in a pluralityof operating states that respectively correspond to various extents oflocal oscillation leakage. The signal strength measuring circuit 23 isused for measuring signal strength of a local oscillation leakagecomponent of an output signal outputted by the power amplifier 22. Thesignal strength measuring circuit 23 includes a rectifier (not shown)and a comparator (not shown). The control signal generating circuit 24outputs a control signal to control the operating state of the mixer 21according to output of the signal strength measuring circuit 23.

During calibration of the mixer 21, for each possible operating state ofthe mixer 21, the power amplifier 22 operates at a higher gain level,and the control signal generating circuit 24 stores information relatedto the operating state and the corresponding signal strength measured bythe signal strength measuring circuit 23. To complete the calibrationprocess, the operating state corresponding to the lowest extent of localoscillation leakage is selected as a current operating state for themixer 21.

Alternatively, during calibration of the mixer 21, the power amplifier22 operates at a higher gain level, and the control signal generatingcircuit 24 changes the current operating state of the mixer 21 insuccession, until the corresponding signal strength measured by thesignal strength measuring circuit 23 is smaller than a preset thresholdvalue, at which time the current operating state of the mixer 21 isfixed.

FIG. 3 illustrates a third conventional transmitter capable of reducinglocal oscillation leakage and I/Q mismatch as disclosed by C. Lee etal., “A Highly Linear Direct-Conversion Transmit Mixer TransconductanceStage with Local Oscillation Feedthrough and I/Q Imbalance CancellationScheme”, Solid-State Circuits, 2006 IEEE International Conference Digestof Technical Papers (San Francisco, U.S.A.), pp. 1450-1459, Feb. 6-9,2006. The third conventional transmitter includes first and seconddigital-to-analog converters 301, 302, first and second low-pass filters303, 304, first and second transconductance stages 305, 306, first andsecond mixers 307, 308, an adder 309, a power amplifier 310, an antenna311, an envelope detector 312, and a variable gain amplifier 313. Firstand second digital base band signals (BBI_(t)), (BBQ_(t)) arerespectively converted into first and second analog radio frequencysignals (RFI_(t)), (RFQ_(t)), which are combined and amplified forsubsequent transmission.

The envelope detector 312 and the variable gain amplifier 313sequentially perform envelope detection and amplification upon an outputsignal of the power amplifier 310 so as to generate a base band ripple.When the first and second digital base band signals (BBI_(t)), (BBQ_(t))are sinusoidal signals with frequencies of (F_(BB)), spectral componentsof the base band ripple appear at (F_(BB)) (due to local oscillationleakage) and (2×F_(BB)) (due to I/Q mismatch). Therefore, spectralanalysis of the base band ripple reveals the extents of localoscillation leakage and I/Q mismatch.

Local oscillation leakage can be categorized into base band localoscillation leakage and radio frequency local oscillation leakage. Baseband local oscillation leakage is attributed to device offsets among thefirst and second digital-to-analog converters 301, 302, the first andsecond low-pass filters 303, 304, and the first and secondtransconductance stages 305, 306. As for radio frequency localoscillation leakage, it arises as a result of direct coupling due toparasitic capacitance or mutual inductance. Reductions of these twodifferent types of local oscillation leakage need to be conductedindependently.

It is noted that the article by C. Lee et al. does not disclose how toadjust the first and second transconductance stages 305, 306 and thephase and amplitude of the first and second digital base band signals(BBI_(t)), (BBQ_(t)) for reducing local oscillation leakage and I/Qmismatch of a transmitter. Neither does the article mention how toreduce local oscillation leakage and I/Q mismatch of a receiver.

SUMMARY OF THE INVENTION

Therefore, an object of the present invention is to provide an adjustingmethod for reducing local oscillation leakage orin-phase/quadrature-phase (I/Q) mismatch in a transmitter.

According to one aspect of the present invention, there is provided anadjusting method for reducing local oscillation leakage or I/Q mismatchin a transmitter. The adjusting method includes the steps of: (a)detecting a current extent of local oscillation leakage or I/q mismatch;(b) determining if an adjusting direction is correct with reference tothe current extent of local oscillation leakage or I/Q mismatch thusdetected, maintaining the adjusting direction if correct, and reversingthe adjusting direction upon determining that the adjusting direction isincorrect; and (c) adjusting a control signal according to the adjustingdirection.

Another object of the present invention is to provide a transmittercapable of reducing local oscillation leakage or I/Q mismatch. Accordingto yet another aspect of the present invention, there is provided atransmitter that includes a mixer, a detecting unit, and an adjustingunit. The mixer mixes a base band signal and a local oscillator signalso as to generate a radio frequency signal. The detecting unit generatesfrom the radio frequency signal a detection signal that represents anextent of local oscillation leakage or I/Q mismatch. The adjusting unitis coupled electrically to the mixer for outputting a control signalthereto to control a current operating state of the mixer. The adjustingunit is further coupled electrically to the detecting unit, anddetermines whether there is a reduction in the extent of localoscillation leakage or I/Q mismatch based on the detection signal fromthe detecting unit. The adjusting unit maintains an adjusting directionfor the control signal upon determining that the extent of localoscillation leakage or I/Q mismatch is reduced, reverses the adjustingdirection upon determining that the extent of local oscillation leakageor I/Q mismatch is not reduced, and adjusts the control signal accordingto the adjusting direction.

Yet another aspect of the present invention is to provide a transmittercapable of reducing in-phase/quadrature-phase (I/Q) mismatch.

According to a further aspect of the present invention, there isprovided a transmitter that includes a compensating unit, first andsecond digital-to-analog converters, first and second low pass filters,first and second mixers, an adder, a detecting unit, and an adjustingunit. The compensating unit performs phase and amplitude compensationupon first and second base band signals so as to generate first andsecond output signals. The first and second digital-to-analog convertersare coupled electrically to the compensating unit for converting thefirst and second output signals received from the compensating unit intocorresponding first and second analog signals, respectively. The firstand second low pass filters are coupled electrically and respectively tothe first and second digital-to-analog converters for performing lowpass filtering respectively upon the first and second analog signals.The first and second mixers are coupled electrically and respectively tothe first and second low pass filters. The first mixer mixes output ofthe first low pass filter with an in-phase local oscillator signal so asto generate a first radio frequency signal. The second mixer mixesoutput of the second low pass filter with a quadrature-phase localoscillator signal so as to generate a second radio frequency signal. Theadder is coupled electrically to the first and second mixers forcombining the first and second radio frequency signals. The detectingunit is coupled electrically to the adder, and generates a detectionsignal that represents an extent of in-phase/quadrature-phase (I/Q)mismatch from output of the adder. The adjusting unit is coupledelectrically to the compensating unit for outputting at least onecontrol signal thereto to control a current operating state of thecompensating unit. The adjusting unit is further coupled electrically tothe detecting unit, and determines whether there is a reduction in theextent of I/Q mismatch based on the detection signal from the detectingunit. The adjusting unit maintains an adjusting direction correspondingto each of the at least one control signal upon determining that theextent of I/Q mismatch is reduced, reverses the adjusting directioncorresponding to each of the at least one control signal upondetermining that the extent of I/Q mismatch is not reduced, and adjustseach of the at least one control signal according to the adjustingdirection corresponding thereto.

BRIEF DESCRIPTION OF THE DRAWINGS

Other features and advantages of the present invention will becomeapparent in the following detailed description of the preferredembodiments with reference to the accompanying drawings, of which:

FIG. 1 is a block diagram of a first conventional transmitter;

FIG. 2 is a block diagram of a second conventional transmitter;

FIG. 3 is a block diagram of a third conventional transmitter;

FIG. 4 is a block diagram of the preferred embodiment of a transmitteraccording to the present invention;

FIG. 5 is a flow chart of an adjusting method for reducing localoscillation leakage and in-phase/quadrature-phase (I/Q) mismatchaccording to the preferred embodiment; and

FIG. 6 is a block diagram of the preferred embodiment of a receiveraccording to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

As shown in FIG. 4, the preferred embodiment of a transmitter accordingto the present invention includes a compensating unit 40, first andsecond digital-to-analog converters 41, 42, first and second low passfilters 43, 44, first and second mixers 45, 46, a first adder 47, adetecting unit 48, and an adjusting unit 49.

The compensating unit 40 performs phase and amplitude compensation uponfirst and second base band signals (BBI_(t), BBQ_(t)) so as to generatefirst and second output signals. The compensating unit 40 is operable ina plurality of operating states that respectively correspond to aplurality of extents of in-phase/quadrature-phase (I/Q) mismatch. Inthis embodiment, the compensating unit 40 includes first and secondvariable gain stages 401, 402, and a second adder 403. The firstvariable gain stage 401 scales the first base band signal (BBI_(t)) by afirst variable (X_(t)) so as to generate the first output signal that isprovided to the first digital-to-analog converter 41. The secondvariable gain stage 402 scales the first base band signal (BBI_(t)) by asecond variable (Y_(t)) so as to generate an intermediate signal. Thesecond adder 403 is coupled electrically to the second variable gainstage 402 for receiving the intermediate signal therefrom, and forcombining the intermediate signal with the second base band signal(BBQ_(t)) so as to generate the second output signal that is provided tothe second digital-to-analog converter 42.

The first and second digital-to-analog converters 41, 42 are coupledelectrically to the compensating unit 40 for converting the first andsecond output signals received from the compensating unit 40 intocorresponding first and second analog signals, respectively. In thisembodiment, the first and second digital-to-analog converters 41, 42 arecoupled electrically and respectively to the first variable gain stage401 and the second adder 403.

The first and second low pass filters 43, 44 are coupled electricallyand respectively to the first and second digital-to-analog converters41, 42 for performing low pass filtering respectively upon the first andsecond analog signals.

The first and second mixers 45, 46 are coupled electrically andrespectively to the first and second low pass filters 43, 44. The firstmixer 45 mixes output of the first low pass filter 43 with an in-phaselocal oscillator signal (LOI_(t)) so as to generate a first radiofrequency signal (RFI_(t)). The second mixer 46 mixes output of thesecond low pass filter 44 with a quadrature-phase local oscillatorsignal (LOQ_(t)) so as to generate a second radio frequency signal(RFQ_(t)). Each of the first and second mixers 45, 46 is operable in aplurality of operating states that respectively correspond to a isplurality of extents of local oscillation leakage.

The first adder 47 is coupled electrically to the first and secondmixers 45, 46 for combining the first and second radio frequency signals(RFI_(t), RFQ_(t)) into a combined radio frequency signal.

The detecting unit 48 is coupled electrically to the first adder 47, andgenerates from output of the first adder 47, i.e., the combined radiofrequency signal, a detection signal that represents an extent of localoscillation leakage and/or an extent of I/Q mismatch. It is noted thatthe frequency of the detection signal is within a base band frequencyrange of the first and second base band signals (BBI_(t), BBQ_(t)). Inthis embodiment, the detecting unit 48 includes a third mixer 481, avariable gain amplifier 482, an analog-to-digital converter 483, and afast Fourier transformer 484. The third mixer 481 receives the combinedradio frequency signal from the first adder 47, and mixes the combinedradio frequency signal with itself. The variable gain amplifier 482 iscoupled electrically between the third mixer 481 and theanalog-to-digital converter 483 for amplifying the output of the thirdmixer 481 prior to receipt by the analog-to-digital converter 483. Theanalog-to-digital converter 483 converts amplified output of thevariable gain amplifier 482 into a corresponding digital signal. Thefast Fourier transformer 484 is coupled electrically to theanalog-to-digital converter 483 for performing fast Fourier transformupon the digital signal from the analog-to-digital converter 483 so asto generate the detection signal that is provided to the adjusting unit49.

When the first and second base band signals (BBI_(t), BBQ_(t)) aresinusoidal signals with frequencies of (F_(BB)), the output of the thirdmixer 481 has spectral components at (F_(BB)) (due to local oscillationleakage) and (2×F_(BB)) (due to I/Q mismatch). In addition, spectralanalysis of the output of the third mixer 481 can reveal the extents oflocal oscillation leakage and I/Q mismatch. It should be noted hereinthat the variable gain amplifier 482 may be optionally omitted in otherembodiments of the present invention. Further, in another embodiment ofthe present invention, the third mixer 481 may be replaced with anenvelope detector (not shown), which receives the combined radiofrequency signal from the first adder 47 and which performs envelopedetection upon the combined radio frequency signal.

The adjusting unit 49 is coupled electrically to the compensating unit40 and to the first and second mixers 45, 46 for outputting at least onecontrol signal thereto to control a current operating state of acorresponding one of the compensating unit 40 and the first and secondmixers 45, 46. In this embodiment, the adjusting unit 49 outputs first,second, third and fourth control signals I(n), Q(n), X(n), Y(n). Theadjusting unit 49 is coupled electrically to the first and second mixers45, 46 for respectively outputting the first and second control signalsI(n), Q(n) to control correspondingly the current operating states ofthe first and second mixers 45, 46, and is further coupled electricallyto the first and second variable gain stages 401, 402 of thecompensating unit 40 for respectively outputting the third and fourthcontrol signals X(n), Y(n) to control correspondingly the first andsecond variables (X_(t), Y_(t)) so as to control the current operatingstate of the compensating unit 40.

With further reference to FIG. 5, the method for reducing localoscillation leakage or I/Q mismatch according to the preferredembodiment of the present invention involves the adjustments ofcorresponding ones of the first to fourth control signals X(n), Y(n),I(n), Q(n). The method includes the following steps.

In step 50, the detecting unit 48 detects one of a current extent oflocal oscillation leakage and a current extent of I/Q mismatch, andgenerates a corresponding detection signal that represents the detectedcurrent extent of local oscillation leakage or I/Q mismatch.

In step 51, the adjusting unit 49 determines, with reference to thecorresponding detection signal, if an adjusting direction correspondingto the detected current extent of local oscillation leakage or I/Qmismatch is correct. If correct, the process jumps to step 53.Otherwise, i.e., upon determining that the adjusting direction isincorrect, the process goes to step 52. In this embodiment, theadjusting direction corresponding to the extent of local oscillationleakage refers to the adjustments made by the adjusting unit 49 to thefirst and second control signals I(n), Q(n), while the adjustingdirection corresponding to the extent of I/Q mismatch refers to theadjustments made by the adjusting unit 49 to the third and fourthcontrol signals X(n), Y(n). Therefore, when the adjusting unit 49determines that there is a reduction in the extent of local oscillationleakage, i.e., when a current extent of local oscillation leakage issmaller than a previous extent of local oscillation leakage, based onthe detection signal from the detecting unit 48, the directions ofadjustments made to the first and second control signals I(n), Q(n) arecorrect. On the other hand, when the adjusting unit 49 determines thatthere is a reduction in the extent of I/Q mismatch, i.e., when a currentextent of I/Q mismatch is smaller than a previous extent of I/Qmismatch, based on the detection signal from the detecting unit 48, thedirections of adjustments made to the third and fourth control signalsX(n), Y(n) are correct.

In step 52, the adjusting unit 49 reverses the adjusting direction.

In step 53, the adjusting unit 49 adjusts the control signalscorresponding to the detected current extent of local oscillationleakage or I/Q mismatch according to the adjusting direction, In thisembodiment, each of the first to fourth control signals I(n), Q(n),X(n), Y(n) is adjusted stepwise by the adjusting unit 49.

In addition to the above steps, the method for reducing one of localoscillation leakage and I/Q mismatch according to the preferredembodiment of the present invention may optionally further include thefollowing steps.

In step 54, the adjusting unit 49 further determines if a terminationcondition is satisfied. If affirmative, the control signalscorresponding to the detected current extent of local oscillationleakage or I/Q mismatch are maintained, and the process is terminated.Otherwise, i.e., upon determining that the termination condition is notsatisfied, the process goes back to step 50 to repeat the determinationas to whether there is a reduction in the detected current extent oflocal oscillation leakage or I/Q mismatch and the adjustment of thecontrol signals corresponding to the detected current extent of localoscillation leakage or I/Q mismatch. In an embodiment of the presentinvention, the adjusting unit 49 determines the termination condition tobe satisfied when the adjusting unit 49 has repeated the determinationas to whether there is a reduction in the detected current extent oflocal oscillation leakage or I/Q mismatch and the adjustment of thecontrol signals corresponding to the detected current extent of localoscillation leakage or I/Q mismatch for a predefined number of times. Inan alternative embodiment of the present invention, the adjusting unit49 determines the termination condition to be satisfied when thedetected current extent of local oscillation leakage or I/Q mismatch isdetermined thereby to be smaller than a predefined threshold.

According to the present invention, the method for reducing localoscillation leakage and I/Q mismatch can be modified such that steps 50to 53 are conducted independently for each of the first to fourthcontrol signals I(n), Q(n), X(n), Y(n) prior to conducting step 54.

In FIG. 6, the preferred embodiment of a receiver according to thepresent invention includes first and second mixers 61, 62, first andsecond low pass filters 63, 64, first and second analog-to-digitalconverters 65, 66, a compensating unit 67, a detecting unit 68, and anadjusting unit 69.

The first mixer 61 mixes an analog radio frequency signal with anin-phase local oscillator signal (LOI_(r)) so as to generate a firstinitial base band signal. The second mixer 62 mixes the analog radiofrequency signal with a quadrature-phase local oscillator signal(LOQ_(r)) so as to generate a second initial base band signal. Each ofthe first and second mixers 61, 62 is operable in a plurality ofoperating states that respectively correspond to a plurality of extentsof local oscillation leakage.

The first and second low pass filters 63, 64 are coupled electricallyand respectively to the first and second mixers 61, 62 for performinglow pass filtering respectively upon the first and second initial baseband signals.

The first and second analog-to-digital converters 65, 66 are coupledelectrically and respectively to the first and second low pass filters63, 64 for converting outputs of the first and second low pass filters63, 64 into corresponding first and second base band signals,respectively.

The compensating unit 67 is coupled electrically to the first and secondanalog-to-digital converters 65, 66 for performing phase and amplitudecompensation upon the first and second base band signals so as togenerate first and second base band output signals. The compensatingunit 67 is operable in a plurality of operating states that respectivelycorrespond to a plurality of extents of I/Q mismatch. In thisembodiment, the compensating unit 67 includes first and second variablegain stages 671, 672, and an adder 673. The first variable gain stage671 scales the first base band signal by a first variable (X_(r)) so asto generate a first intermediate signal. The second variable gain stage672 scales the second base band signal by a second variable (Y_(r)) soas to generate a second intermediate signal. The adder 673 is coupledelectrically to the first and second variable gain stages 671, 672 forcombining the first and second intermediate signals therefrom so as togenerate the first base band output signal (BBI_(r)). The compensatingunit 67 outputs the second base band signal from the secondanalog-to-digital converter 66 as the second base band output signal(BBQ_(r)).

The detecting unit 68 is coupled electrically to the compensating unit67 for generating the detection signal that represents an extent oflocal oscillation leakage and/or an extent of I/Q mismatch from thefirst and second base band output signals (BBI_(r), BBQ_(r)). In thisembodiment, the detecting unit 68 includes a fast Fourier transformer681 that performs fast Fourier transform upon the first and second baseband output signals (BBI_(r), BBQ_(r)) from the compensating unit 67 togenerate a detection signal that represents an extent of localoscillation leakage and/or an extent of I/Q mismatch. In particular, thefast Fourier transformer 681 treats the first and second base bandoutput signals (BBI_(r), BBQ_(r)) as a complex signal(BBI_(r)+j×BBQ_(r)). If an ideal analog radio frequency signal does nothave local oscillation leakage and/or I/Q mismatch, e.g., when theanalog radio frequency signal is generated by a transmitter capable ofreducing local oscillation leakage and/or I/Q mismatch such as thetransmitter of the preferred embodiment, and when the first and secondbase band output signals (BBI_(r), BBQ_(r)) are sinusoidal signals withfrequencies of (F_(BB)), the first and second base band output signals(BBI_(r), BBQ_(r)) have spectral components at DC (due to localoscillation leakage) and (-F_(BB)) (due to I/Q mismatch). In addition,spectral analysis of the first and second base band output signals(BBI_(r), BBQ_(r)) reveals the extents of local oscillation leakage andI/Q mismatch.

The adjusting unit 69 is coupled electrically to the first and secondmixers 61, 62 and the first and second variable gain stages 671, 672 ofthe compensating unit 67 for respectively outputting first to fourthcontrol signals I(n), Q(n), X(n), Y(n) thereto to respectively controlcurrent operating states of the first and second mixers 61, 62 and thefirst and second variables (X_(r), Y_(r)) of the first and secondvariable gain stages 671, 672, i.e., a current operating state of thecompensating unit 67.

Since operation of the adjusting unit 69 is similar to that of theadjusting unit 49 (as shown in FIG. 4), further details of the same areomitted herein for the sake of brevity.

It should be noted herein that since each of the adjusting unit 49 ofthe transmitter and the adjusting unit 69 of the receiver according tothe preferred embodiment of the present invention is capable ofreceiving the detection signal that represents the extents of localoscillation leakage and/or I/Q mismatch and that are presenteddigitally, the present invention is easy to implement.

While the present invention has been described in connection with whatare considered the most practical and preferred embodiments, it isunderstood that this invention is not limited to the disclosedembodiments but is intended to cover various arrangements includedwithin the spirit and scope of the broadest interpretation so as toencompass all such modifications and equivalent arrangements.

1. An adjusting method for reducing local oscillation leakage orin-phase/quadrature-phase (I/Q) mismatch in a transmitter, saidadjusting method comprising the steps of; (a) detecting a current extentof local oscillation leakage or I/Q mismatch: (b) determining if anadjusting direction is correct with reference to the current extent oflocal oscillation leakage or I/Q mismatch thus detected, maintaining theadjusting direction if correct, and reversing the adjusting directionupon determining that the adjusting direction is incorrect; and (c)adjusting a control signal according to the adjusting direction.
 2. Theadjusting method as claimed in claim 1, wherein the adjusting directionis determined to be correct when the current extent of local oscillationleakage or I/Q mismatch is smaller than a previous extent of localoscillation leakage or I/Q mismatch.
 3. The adjusting method as claimedin claim 1, wherein the control signal is adjusted stepwise in step (c).4. The adjusting method as claimed in claim 1, further comprising thesteps of determining if a termination condition is satisfied, andrepeating steps (a) to (c) upon determining that the terminationcondition is not satisfied.
 5. The adjusting method as claimed in claim4, wherein the termination condition is determined to be satisfied whensteps (a) to (c) have been repeated for a predefined number of times. 6.The adjusting method as claimed in claim 4, wherein the terminationcondition is determined to be satisfied when the current extent of localoscillation leakage or I/Q mismatch is smaller than a predefinedthreshold.
 7. A transmitter comprising; a first mixer for mixing a baseband signal and a local oscillator signal so as to generate a radiofrequency signal; a detecting unit for generating from the radiofrequency signal a detection signal that represents an extent of localoscillation leakage or in-phase/quadrature-phase (I/Q) mismatch; and anadjusting unit coupled electrically to said first mixer for outputting acontrol signal thereto to control a current operating state of saidfirst mixer, said adjusting unit being further coupled electrically tosaid detecting unit, and determining whether there is a reduction in theextent of local oscillation leakage or I/Q mismatch based on thedetection signal from said detecting unit; wherein said adjusting unitmaintains an adjusting direction for the control signal upon determiningthat the extent of local oscillation leakage or I/Q mismatch is reduced,reverses the adjusting direction upon determining that the extent oflocal oscillation leakage or I/Q mismatch is not reduced, and adjuststhe control signal according to the adjusting direction.
 8. Thetransmitter as claimed in claim 7, wherein said first mixer is operablein a plurality of operating states that respectively correspond to aplurality of extents of local oscillation leakage or I/Q mismatch. 9.The transmitter as claimed in claim 7, wherein frequency of thedetection signal is within a base band frequency range of the base bandsignal.
 10. The transmitter as claimed in claim 7, wherein the controlsignal is adjusted stepwise by said adjusting unit.
 11. The transmitteras claimed in claim 7, wherein said adjusting unit further determines ifa termination condition is satisfied, and repeats the determination asto whether there is a reduction in the extent of local oscillationleakage or I/Q mismatch and the adjustment of the control signal upondetermining that the termination condition is not satisfied.
 12. Thetransmitter as claimed in claim 11, wherein said adjusting unitdetermines the termination condition to be satisfied when said adjustingunit has repeated the determination as to whether there is a reductionin the extent of local oscillation leakage or I/Q mismatch and theadjustment of the control signal for a predefined number of times. 13.The transmitter as claimed in claim 11, wherein said adjusting unitdetermines the termination condition to be satisfied when the extent oflocal oscillation leakage or I/Q mismatch is determined thereby to besmaller than a predefined threshold.
 14. The transmitter as claimed inclaim 7, wherein said detecting unit includes a second mixer forreceiving the radio frequency signal from said first mixer and formixing the radio frequency signal with itself, an analog-to-digitalconverter for converting output of said second mixer into acorresponding digital signal, and a fast Fourier transformer coupledelectrically to said analog-to-digital converter for performing fastFourier transform upon the digital signal from said analog-to-digitalconverter so as to generate the detection signal that is provided tosaid adjusting unit.
 15. The transmitter as claimed in claim 14, whereinsaid detecting unit further includes a variable gain amplifier coupledelectrically between said second mixer and said analog-to-digitalconverter for amplifying the output of said second mixer prior toreceipt by said analog-to-digital converter.
 16. The transmitter asclaimed in claim 7, wherein said detecting unit includes an envelopedetector for receiving the radio frequency signal from said first mixerand for performing envelope detection upon the radio frequency signal,an analog-to-digital converter for converting output of said envelopedetector into a corresponding digital signal, and a fast Fouriertransformer coupled electrically to said analog-to-digital converter forperforming fast Fourier transform upon of the digital signal from saidanalog-to-digital converter so as to generate the detection signal thatis provided to said adjusting unit.
 17. The transmitter as claimed inclaim 16, wherein said detecting unit further includes a variable gainamplifier coupled electrically between said envelope detector and saidanalog-to-digital converter for amplifying the output of said envelopedetector prior to receipt by said analog-to-digital converter.
 18. Atransmitter comprising: a compensating unit for performing phase andamplitude compensation upon first and second base band signals so as togenerate first and second output signals; first and seconddigital-to-analog converters coupled electrically to said compensatingunit for converting the first and second output signals received fromsaid compensating unit into corresponding first and second analogsignals, respectively; first and second low pass filters coupledelectrically and respectively to said first and second digital-to-analogconverters for performing low pass filtering respectively upon the firstand second analog signals; first and second mixers coupled electricallyand respectively to said first and second low pass filters, said firstmixer mixing output of said first low pass filter with an in-phase localoscillator signal so as to generate a first radio frequency signal, saidsecond mixer mixing output of said second low pass filter with aquadrature-phase local oscillator signal so as to generate a secondradio frequency signal; a first adder coupled electrically to said firstand second mixers for combining the first and second radio frequencysignals; a detecting unit coupled electrically to said first adder, andgenerating a detection signal that represents an extent ofin-phase/quadrature-phase (I/Q) mismatch from output of said firstadder; and an adjusting unit coupled electrically to said compensatingunit for outputting at least one control signal thereto to control acurrent operating state of said compensating unit, said adjusting unitbeing further coupled electrically to said detecting unit, anddetermining whether there is a reduction in the extent of I/Q mismatchbased on the detection signal from said detecting unit; wherein saidadjusting unit maintains an adjusting direction corresponding to each ofsaid at least one control signal upon determining that the extent of I/Qmismatch is reduced, reverses the adjusting direction corresponding toeach of said at least one control signal upon determining that theextent of I/Q mismatch is not reduced, and adjusts each of said at leastone control signal according to the adjusting direction correspondingthereto.
 19. The transmitter as claimed in claim 18, wherein saidcompensating unit is operable in a plurality of operating states thatrespectively correspond to a plurality of extents of I/Q mismatch. 20.The transmitter as claimed in claim 18, wherein frequency of thedetection signal is within a base band frequency range of the first andsecond base band signals.
 21. The transmitter as claimed in claim 18,wherein each of said at least one control signal is adjusted stepwise bysaid adjusting unit.
 22. The transmitter as claimed in claim 18, whereinsaid adjusting unit further determines if a termination condition issatisfied, and repeats the determination as to whether there is areduction in the extent of I/Q mismatch and the adjustment of each ofsaid at least one control signal upon determining that the terminationcondition is not satisfied.
 23. The transmitter as claimed in claim 22,wherein said adjusting unit determines the termination condition to besatisfied when said adjusting unit has repeated the determination as towhether there is a reduction in the extent of I/Q mismatch and theadjustment of each of said at least one control signal for a predefinednumber of times.
 24. The transmitter as claimed in claim 22, whereinsaid adjusting unit determines the termination condition to be satisfiedwhen the extent of I/Q mismatch is determined thereby to be smaller thana predefined threshold.
 25. The transmitter as claimed in claim 18,wherein: said adjusting unit generates first and second ones of thecontrol signals; and said compensating unit includes a first variablegain stage for scaling the first base band signal by a first variable soas to generate the first output signal that is provided to said firstdigital-to-analog converter, a second variable gain stage for scalingthe first base band signal by a second variable so as to generate anintermediate signal, and a second adder coupled electrically to saidsecond variable gain stage for receiving the intermediate signaltherefrom, and for combining the intermediate signal with the secondbase band signal so as to generate the second output signal that isprovided to said second digital-to-analog converter, wherein said firstand second variable gain stages are coupled to said adjusting unit, andrespectively receive the first and second ones of the control signalsfor controlling correspondingly the first and second variables.